Modern guided missiles need high performance solid propellant gas generators for providing high pressure and high temperature gases to the control nozzles of post boost control systems and the like. Prior art thermal insulations have not provided the high performance required for advanced weapon systems that must undergo severe operating requirements having long duration propellant burn requirements at very high pressures and temperatures. The primary requirements for thermal insulation of missile system high temperature solid propellant gas generators include high heat flow resistance; erosion resistance; producibility including bonding, layout, machining, dimensional control, mixing and calendaring; aging stability; system chemical compatibility; and non-toxicisity. In order to minimize toxic health hazards it has been necessary to use suitable non-toxic insulation materials in place of asbestos. Solutions to these and other requirements have been accomplished by the thermal insulation composition of the present invention.